In this exercise, researchers are studying the effect of a new fertilizer compared to no fertilizer on plant growth. They randomly select 80 plants from the same species and assign the two treatments to 40 plants each. The researchers measure the height and number of leaves of the plants after two months to assess the impact of the new fertilizer.
Study A
We can specify the above design using edibble package in R as below. What do you notice about the treatment allocation? Could this be problematic? Why?
Study B
You’ve been told that the plants are grouped into 4 blocks where each block contains 20 pots. One plant is grown in each pot. The researchers want to make sure that each block has an equal number of plants from each treatment group. They also want to randomize the treatment allocation within each block. How would you design this experiment? Using tidyverse or otherwise, count how many plants are assigned to each treatment group within each block after you have your design layout.
Sample solution
Study C
You’ve now been told that the researchers want an additional temperature (standard or high) treatment factor. But they also tell you that they can’t change the temperature for each pot. Instead, they can only change the temperature for each block. How would you design this experiment? Using tidyverse or otherwise, get the treatment replications.